1. Field of the Invention
The present invention generally relates to a semiconductor device and a method for manufacturing the same, and more particularly to a semiconductor device having a structure of coating an edge of a connection hole of a metal pattern layer among plural metal pattern layers with a passivation layer, the metal pattern layer which will be a chip pad, and a method for manufacturing the same.
2. Description of the Related Arts
Semiconductor devices are fabricated on a silicon substrate using successive steps of photolithography, etching, diffusion, and deposition.
A deposition step refers to a kind of the material synthesis process, in which a desired thin layer is obtained by changing a specific element or compound from the source in a gas or vapor phase into a solid phase. In the manufacturing of the semiconductor device, thin layers of silicon oxide, silicon nitride, various metals and/or suicide are required. All the thin layers are obtained by the deposition step.
The deposition step is also referred to as a thin film formation process, and is divided includes two methods, that is, a PVD (Physical Vapor Deposition) and a CVD (Chemical Vapor Deposition). The physical vapor deposition is a deposition method, in which a desired thin layer is deposited only by changing a phase of the source, without adding or omitting other components to or from the source. On the other hand, chemical vapor deposition includes the chemical reactions, so there are differences in a physical and a chemical structure between the kind of source and the deposited product. Generally, a sputtering method is used for the physical vapor deposition.
Among the above-described deposition steps, a metallization step means a metal wiring step, in which aluminum (Al) with the thickness of about 6,000 .ANG. is deposited on the silicon substrate to electrically interconnect a plurality of the semiconductor devices foiled on the upper surface of the silicon substrate to each other, and to form chip pads for electrically connecting the semiconductor devices to external circuitry.
A method for manufacturing a semiconductor device using a conventional deposition step will be described hereinafter, with reference to FIG. 1 through FIG. 4.
FIG. 1 schematically shows a coating of a passivation layer 17 on an upper surface of a silicon substrate 10, where a plurality of metal pattern layers 12, 14 are formed, in order to manufacture a plurality of semiconductor devices (30 in FIG. 4) on the silicon substrate 10, and FIG. 2 is a cross-sectional view taken along the line 2--2 in FIG. 1. With reference to FIG. 1 and FIG. 2, a first metal pattern layer 12 is deposited on the upper surface of the silicon substrate 10. And, the first metal pattern layer 12 is electrically insulated from a second metal pattern layer 14 by interposing an inter metal dielectric 16(IMD) between the first metal pattern layer 12 and the second metal pattern layer 14. To electrically interconnect the first metal pattern layer 12 to the second metal pattern layer 14, a connection hole 15 is formed by selectively removing, the inter metal dielectric 16 on a designated portion. A designated portion of the second metal pattern layer 14 is used as a chip pad (19 in FIG. 4). The upper surface of the silicon substrate including an upper surface of the second metal pattern layer 14 is coated with the passivation layer 17.
Herein, the first metal pattern layer 12 is formed by successively depositing a Ti/TiN layer 12b, an Al layer 12a, and a TiN layer 12c on the upper surface of the silicon substrate 10. The second metal pattern layer 14 is formed by successively depositing a Ti layer 14b and an Al layer 14a on an upper surface of the Al layer 12a of the first metal pattern layer 12. Generally, all the layers are deposited by sputtering. The TiN layer 12c of the first metal pattern layer 12 is positioned between the lower surface of the inter metal dielectric 16 and the upper surface of the Al layer 12a of the first metal pattern layer 12, and the Ti/TiN layer 12b of the first metal pattern layer 12 is used as a barrier metal layer.
The connection hole 15 is formed by selectively removing a portion of the inter metal dielectric 16 after depositing the first metal pattern layer 12 and the inter metal dielectric 16 on the silicon substrate 10. Consequently, the upper surface of the silicon substrate 10 including the first metal pattern layer 12 and the inter metal dielectric 16 is uneven and stepwise. Therefore, the second metal pattern layer 14 deposited on the upper surfaces of the first metal pattern layer 12 and the inter metal dielectric 16, is formed with the uneven thickness. Described in more detail, a concave corner 14c is formed along an edge 13, where the first metal pattern layer 12 is in contact with the inter metal dielectric 16, in which the second metal is thinner in the thickness than that of any other portion of the second metal pattern layer 14. Accordingly, the concave corner 14c having a bad step coverage is formed on the edge 13, where the first metal pattern layer 12 is in contact with the inter metal dielectric 16.
The reason that the concave corner 14c is formed on the second metal pattern layer 14 will be described hereinafter. The second metal pattern layer 14 is deposited on the upper surfaces of the first metal pattern layer 12 including the connection hole 15, and the inter metal dielectric 16 by sputtering. In sputtering, Ar atoms are accelerated and collide with a target in the vacuum condition. In the present invention, the target is made of an Al (Aluminum) and a Ti (Titanium) plate. Molecules of the target material are broken off by the colliding of the Ar atoms and deposited on the upper surface of the silicon substrate 10. At this time, the number of the particles of the components of the target, which is deposited on the vertical surface of the silicon substrate 10 to the target, is fewer than that of the components, which is deposited on the horizontal surface of the silicon substrate 10 to the target. Particularly, the number of the particles of target material deposited on the edge 13, on which the first metal pattern layer 12 is in contact with the inter metal dielectric 16, is fewer than that of the target material deposited on any other portion of the silicon substrate 10. As described above, since the number of the particles of target material deposited on the edge 13 is fewest, the concave corner 14c of the second metal pattern layer 14 is indented toward the edge 13.
The passivation layer 17 is composed of PEOX (Plasma Enhanced silicon Oxide) and silicon nitride (Si3N4). Reference numeral 17a refers to a point or boundary for etching the passivation layer 17 to expose a portion of the second metal pattern layer 14 to the outside, the portion which will be a chip pad (19 in FIG. 4), that is, the chip pad portion of the second metal pattern layer 14. The etched point 17a is disposed along an outer periphery of the connection hole 15.
Then, a photo-etching step is carried out for removing a portion of the passivation layer 17 on the upper surface of the second metal pattern layer 14 to expose the chip pad portion of the second metal pattern layer 14 to the outside. As shown in FIG. 3, an upper surface of the passivation layer 17 is coated with a photoresist 18 and a developing step is carried out for removing the photoresist 18 of the upper surface of the chip to expose the pad portion of the second metal pattern layer 14. After that, as shown in FIG. 4, a portion of the passivation layer 17 is removed from the upper surface of the chip pad portion of the second metal pattern layer 14 by the dry etching method, and an ashing/strip step is carried out for removing the photoresist 18 remaining on the silicon substrate 10. Accordingly, a semiconductor device 30, on which a plurality of the chip pads are formed on the silicon substrate 10 by partially exposing the Al layer 14a of the second metal pattern layer 14, is manufactured. Herein, a boundary or point 18a in FIG. 3, where a pad pattern of the photoresist 18 is formed by developing the photoresist 18, coincides with the etched boundary or point 17a in FIG. 1. The chip pad 19 includes a portion of the second metal pattern layer 14, the portion contacting the upper surface of the first metal pattern layer 12, and partially another portion of the second metal pattern layer 14, positioned on the upper surface of the inter metal dielectric 16 along the periphery of the connection hole 15.
The semiconductor device 30 which is manufactured by the above-described steps has several problems as follows. Since the concave corner 14c is exposed to the outside during the photo-etching and the ashing step for removing the photoresist 18, it may be attacked due to its relative thin thickness and a failure such as separation of the Al layer 14a along the concave corner 14c may occur. After that, chemicals used in the strip step for removing the photoresist 18 may react with the Ti layer 14b under the cutting Al layer 14a, contaminating or damaging the Ti layer 14b.
Also, under the baking process following the formation of the protective layer such as a polyimide layer (not shown in FIG. 4), a failure such as separation of the Al layer 14a along the concave corner 14c with relatively thin thickness may occur. Therefore, during the ball bonding process after the manufacturing of the semiconductor device, the Al layer 14a of the second metal pattern layer 14 separate and exfoliate or peel from the Al layer 12a of the first metal pattern layer 12.